This invention relates to breathing devices for assisting patients, particularly human patients, to breathe by maintaining a positive airway pressure during the breathing cycle.
It is well recognised that the application of continuous positive airways pressure (CPAP) is a successful clinical technique for assisting patients with breathing difficulties. Recently a particularly successful non-invasive CPAP device has been described in EP-A-0447 443 and marketed by the Applicant as the INFANT FLOW (registered trade mark) generator. This device has been shown to deliver reliable CPAP whilst at the same time resulting in a lower work of breathing when treating respiratory distress syndrome. This lower work of breathing is important as it leads to faster patient recovery times which is of course beneficial to the patient, but which also helps to keep down running costs of intensive care departments.
It has been recognised that the phenomenon of jet bypass, whereby a proportion of fresh gas supplied to the patient passes directly out of the exhaust tube is crucial in giving the low added work of breathing.